1. Technical Field
The present invention relates to a method for producing an organic acid such as succinic acid using a bacterium.
2. Background Art
For the production of non-amino organic acids, including succinic acid, by fermentation, anaerobic bacteria are typically used, including bacteria belonging to the genus Anaerobiospirillum or Actinobacillus (U.S. Pat. Nos. 5,142,834 and 5,504,004, International Journal of Systematic Bacteriology (1999), 49, 207-216). Although such anaerobic bacteria provide high yields of products, many nutrients are required for their proliferation, and therefore it is necessary to add large amounts of organic nitrogen sources such as corn steep liquor (CSL) into the culture medium. The addition of large amounts of sources of organic nitrogen results in not only an increase in cost for the culture medium, but also an increase in the purification costs for isolating the product, and therefore it is not economical.
In addition, methods are known in which aerobic bacteria such as coryneform bacteria are cultured once under aerobic conditions to proliferate the bacterial cells, then the cells are harvested, washed, and allowed to rest so that a non-amino organic acid is produced without having to supply oxygen (Japanese Patent Laid-open (KOKAI) Nos. 11-113588 and 11-196888). These methods are economical, since organic nitrogen can be added in a smaller amount for proliferation of the bacterial cells, and the bacteria can sufficiently grow in a simple culture medium. However, there is still a room for improvement in terms of production amounts, concentration, and production rate per cell of the target organic acids as well as simplification of the production process, and the like. Furthermore, production of a non-amino organic acid by fermentation using a bacterium in which phosphoenolpyruvate carboxylase activity is enhanced (for example, Japanese Patent Laid-open No. 11-196887), and the like, has also been reported.
Furthermore, in the facultative anaerobic gram negative bacterium Escherichia coli, methods are known for producing a non-amino organic acid by culturing it once under aerobic conditions to allow for the growth of cells, and then culturing the resting cells without supplying oxygen to anaerobically produce the non-amino organic acid (Journal of Industrial Microbiology and Biotechnology (2002), 28 (6), 325-332), which is similar to the methods using coryneform bacteria. Also, the Escherichia coli bacteria can be aerobically cultured to aerobically produce the non-amino organic acid (U.S. Patent Published Application No. 20050170482). However, since Escherichia coli is a gram negative bacterium, it is vulnerable to osmotic pressure, and there remains room for improvement in productivity per cell etc.
The entire genome sequence of Escherichia coli, which belongs to the Enterobacteriaceae family, has been reported, and functions of putative protein-coding sequences have been predicted. The yidE gene is one of these putative protein-coding sequences, and although it is thought to code for a transporter, the actual function of this gene has not been clarified. Finally, the role of this gene in organic acid production has not been previously reported Nucleic Acid Research (2006), 34 (1), 1-9; Applied and Environmental Microbiology (2005), 71 (12), 8008-8015).